We consider a dark halo with a visible galaxy inside. The first consists mainly of DM while the second consists mainly of BM. Let us assume that both of these components are spherically symmetric, so that the total matter density \(\rho \)  depends only on the radius \(r\) . This greatly simplifies the model, but contradicts the results of \(N\) -body simulations described, e.g., in §9.3.3 in [1]}. Spherical symmetry does certainly not apply to BM in spiral galaxies. However, it is reasonable to consider this simplified model, because the dominant part of the mass of the galaxy \(M\)  is associated with the halo. The halo mass is about 85% of the total mass for a typical galaxy.
